The best anonymous altcoin is Zcash. In fact, Zcash is the first truly anonymous currency. The main Zcash feature is mathematically guaranteed anonymity. Zcash guarantees complete anonymity, unlike the rather transparent Bitcoin, where the movement of money is tracked with absolute accuracy. In the current conditions of attempts of strict state control over citizens in different countries, Zcash is a currency that will be in demand by society.
Zcash has a trusted setup that could create an unlimited amount of undetectable zcash coins. This kills zcash from ever amounting to anything grandious FULL STOP. This will never be accepted.
Zcoin is the best option due to auditable supply and similar anonymity. The trade off is visible tx amounts, but thats not nearly as bad as an invisible dictator. Also hurts investor confidence for Zcash having this weakness.